Case Study - Superweight Liner

The Product/ServiceSuperweight PTFE Lined Piping CustomerCrop Protection Products Manufacturer The Problem The manufacturing process for one the sites key product ranges involved the movement of a cocktail of solvents at both high temperature and pressure. The particular mixture led to a rapid corrosion of high nickel alloys. The alternative solution had been conventional PTFE and PFA lined piping. However, for materials prone to permeation, temperature and pressure are good drivers and in the space of months, permeation occurred. This alone would not have been an issue, but the permeant materials on contact with the atmosphere at the vent points solidified into a tar like substance, effectively blocking the venting arrangement. This in turn pressurised the outside of the liners and led to full or partial collapse of the lining within spools. The SolutionCRP has always manufactured their pipe liners using paste extrusion which of all the PTFE processing methods has the highest resistance to permeation. A like for like wall thickness of paste extruded PTFE performs significantly better in duties that are susceptible to permeation than an equivalent thickness of isostatically moulded pipe liner. However in duties such as this even PTFE will permeate eventually. A second line of defence is to increase the standard wall thickness of the liners, particularly in the smaller nominal bores sizes, which tend to have thinner standard liners. The effect of wall thickness is to reduce the “driving” effect of temperature and pressure and either cause the permeation to arrive at an equilibrium point within the liner thickness as it permeates, or to continue to slow the rate of permeation. CRP manufactured a range of “superweight” lined piping for the customer and this has had a beneficial effect on the rate of permeation through the linings. This coupled with an inspection regime for blocked venting has had a significant effect on reducing the effects of permeation on the plant. It is worth noting that the PFA lined fittings in which CRP specialises performed well and CRP did not need to supply anything beyond the standard product.

PTFE lined pipe showing collapse due to permeant pressure.

PFA lined fitting showing blistering and attack from permeant, but continuing to perform in service.